"The tensions are very high and will continue to be high," said Jamal Daoud, a Shia community leader in Sydney, where a 47-year old Shia leader was shot in the shoulder early Monday morning, as worshipers observed the Shia ritual of Ashura.

He said Rasoul Al Mousawi, a leader in the Shia community focused around the Islamic center in Greenacre, south-west Sydney, had been released from hospital on Tuesday and was doing well.

The attack was only one incident in a string of attacks and threats against Shia Muslims by Sunni extremists who sympathized with ISIS, he claimed, and had followed an incident where a group of men had driven past the Islamic center, yelling comments such as "IS lives forever" and "Shia dogs" in Arabic.

A security guard had also been attacked by a group of men who appeared to be followers of the austere Wahhabi tradition of Sunni Islam on Friday, he said.

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"There's high tension between Sunni and Shia, but these extremists, they threaten and attack Sunnis too," he said.

"Anyone who speaks against the fighting in Syria and advocating the government to take action against people in Iraq and Syria -- they are threatened and attacked."

Jamal Rifi, a Sydney-based GP and Sunni community leader, agreed, saying sectarian tensions were at an unprecedented level as a result of the brutal Syrian conflict, and the appeal of ISIS to radicalized Sunni youth in Australia.

On Tuesday, Australian Prime Minister Tony Abbott told reporters that "it seems there is an ISIL death cult influence on this shooting in Sydney," using an alternative name for the terror group. "The important thing is for all of us to absolutely reject this death cult," he said.

Some Australian media reports suggested a leadership dispute at the Islamic center could have been the reason behind the attack, but Daoud rejected the notion, saying the dispute was being litigated in the courts and it was highly unlikely that it would take a violent turn.

A New South Wales police spokesman said there was nothing to add beyond the police's initial statement calling for public information on the shooting.

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During previous periods when Australian Muslims had felt under attack -- such as in the wake of the September 11 attacks, the Bali bombings or the Cronulla riots -- they had bonded together under a common identity.

But now many in the community felt doubly under fire -- from sectarian agitators and from "rednecks" in the wider public, said Daoud.

Rifi said that from the early days of the Syrian conflict, Sunni extremists had inflamed community tensions by attempting to "name and shame" businesses on social media that were run by members of Alawite sect, to which Syrian President Bashar al-Assad belongs.

"They will use any excuse to create division," he said.

Rifi said he remained optimistic. "The forces that pull us apart are increasing in strength, but they are nowhere as strong as the forces that pull us together," he said.

But Daoud did not believe things would improve soon.

"It is a very tough time, and we expect it to become more tough," he said.